Jin Yong didn't juse change his opinion on Yang Guo's sword skills.
He changed his opinion on Dugu Qiubai's sword progression as well.
In fact like bliss (and maybe even you) said, Jin Yong changed his entire philosophy on swordsmanship.
Were it just a matter of Yang Guo's swordplay, it wouldn't be a big deal.
But now what we have are inconsistent models of Demonic Swordsman Dugu Qiubai! In ROCH he was a person who relied on internal energy and possibly speed. There was NOTHING in ROCH that said Dugu Qiubai did anything resembling "no technique overcomes technique". But in SPW, he was a person who thrived on something more sophisticated.
In ROCH, Dugu Qiubai's model was: Overcoming the sword without a sword.
In SPW, Dugu Qiubai's model was: Overcoming technique without technique OR sword.
Yes, I do agree that the SPW model of Dugu Qiubai seems to be more mature and more savvy.
But then, the question is, if Jin Yong had a different vision for Dugu Qiubai, why didn't he just change the person into somebody else. Why did he stick with using the same guy for make him inconsistent with ROCH? You see, this is my beef with Jin Yong. He probably should have just picked a whole new character. Maybe even one of Dugu Qiubai's rivals' sons or something who overcame Dugu Qiubai's theories...